Slide valves may be used in pipeline systems for distributing and/or handling fluid such as water, sewages, natural gas or similar liquid or gaseous media. A slide valve comprises a housing defining a passage way for the fluid to flow in an axial direction to the housing. The passage may be closed and open by sliding the valve wedge in a direction transverse to the axial direction. Typically, the plane of the sliding movement of the valve wedge is essentially perpendicular to the axial direction. The motion of the valve wedge is actuated by actuation means. The actuation means may comprise a threaded valve stem configured to act upon a valve nut to produce a linear translational movement of the sliding of the slide wedge into or out of the passage way of the housing.
Under operation, the valve wedge is subjected to considerable pressure in the axial direction. In order to take up these axial pressures sliding bearings comprising the guide members projecting into the corresponding guide grooves in the valve housing are provided. The guide grooves are shaped complimentary to the shape of the guide members so as to provide guidance at least in axial direction.
In a slide valve in a soft sealing type, a sealing is provided by the soft sealing material, typically a rubber material, engaging a valve seat, which may be a dedicated valve seal element or simply a wall of the valve housing. The material of the core of the valve wedge is typically cast iron, which is prone to degradation/corrosion when exposed to a fluid passing through the valve. Therefore, the soft sealing encapsulation is provided for purposes of improving corrosion protection of the core. The ribs of the core may also be covered with the soft sealing material. However, the problem of such a solution is that the soft sealing material is typically not wear-resistant with respect to a sliding motion. Further, typical soft sealing material has a high friction coefficient with respect to most surfaces. This problem may be solved by using slide shoes arranged on the guide ribs, wherein the slide shoes are preferably made of a wear-resistant and corrosion-resistant material providing a low friction sliding interface with a sliding surface of a cooperating guide groove.
EP0171693 discloses a slide valve with a valve wedge comprising guide shoes that are attached to the valve wedge core and molded together with a rubber encapsulation of the valve wedge. The problem with this solution is that the slide shoes, which are supported by a relatively thick, soft layer of soft seal material, prevent a precise control over the valve member movement as the slide shoes may flex laterally relative to the core, whereby the life of the valve wedge may be decreased.
EP0926410 discloses a slide valve wedge, wherein a slide shoe is attached to the ribs of the core after the soft sealing encapsulation has been molded onto the core. The problem with this solution is that the slide shoes supported by the soft layer prevent a precise control over the valve wedge movement as the guide shoes may flex laterally. In particular under large axial pressure on the valve wedge such flexing on the shoes may result in an excessive wear of the valve actuation mechanism as well as the sealing surfaces. Furthermore, when applying a soft seal encapsulation to a valve wedge, the valve wedge core is typically supported by centering pins during molding in order to center the core in the mold. These centering pins leave openings in the soft seal encapsulation, thus requiring a subsequent sealing step for these openings.
DE3345133 discloses a valve wedge for a slide valve comprising a metal core encapsulated in a rubber elastic material. The metal core is provided with lateral guiding grooves in each of which a U-shaped sliding shoe of plastic material is arranged so that a gap or hollow space is formed between the sliding shoes and the guiding grooves. The gap or hollow space is filled with molding mass of rubber elastic material during molding of the encapsulation onto the metal core. The sliding shoes are supported by the soft rubber elastic material preventing a precise control over the valve wedge movement, especially at the large axial pressures on the valve wedge.